Real-life noise may consist of different types of noises: stationary and non-stationary noises. Non-stationary noise may include two classes of noise: an abrupt increase of noise floor and an impulsive noise. Both are particularly challenging to deal with respect to audio processing where a noise signal is concerned. As used herein, an abrupt increase of noise floor refers to the noise floor suddenly increasing from one level to another level and maintaining substantially stationary during a relative long period of time, Impulsive noise refers to a non-stationary noise when the level increases suddenly and then drops down within a short period of time. Usually, in audio processing, such as speech enhancement, audio play, or noise compensation, the noise level is required to be tracked. For example, in headphone noise compensation, the estimated level of a noise signal may directly impact the gain applied to the audio signal. The actual signal level of a noise signal generally cannot be applied as it changes rapidly over time, especially when an abrupt increase of noise floor or an impulsive noise occurs. As such, a noise signal input should be processed to obtain an estimated noise level that can be used in audio processing, as illustrated in FIG. 1.
Noise estimation techniques have been developed mainly in the framework of speech processing, especially in speech enhancement. These techniques, for example, may be divided into minimum tracking, time-recursive averaging, histogram based noise estimation, and quantile based noise estimation and so on. Concerning the two classes of non-stationary noises, the estimated noise level is desired to follow the abrupt increase of noise floor and to resist a drift of noise estimation during the short-period impulsive noise. However, the existing noise estimation methods are either too sensitive to the abrupt increase of noise floor or too sensitive to the impulsive noise, thereby disabling the estimate of a robust level of noise in these two noise scenarios.
In view of the foregoing, there is a need in the art for a solution for appropriately estimating noise levels for both impulsive noises and the abrupt increasing of a noise floor.